1. Field of the Invention
This invention relates generally to medical equipment used in thoracic medicine and more specifically to thorax drainage apparatuses.
2. Description of the Prior Art
It is necessary to drain air and fluid from the pleural space following operation or injury to organs within the thorax. If drainage of air and fluid from the pleural space is not sufficient, the lung will not be able to expand to fill the pleural space which may result in respiratory insufficiency or the development of infection. Many different types of drainage devices have been provided for draining the pleural space. One method of draining the pleural space is to insert a catheter into the chest with the distal end thereof sealed by a condom having the end removed, to a complicated system of up to five serially connected chambers having constricted connections. In the later systems, now the state of the art, a problem arises when there is a high volume air leak from the lung which is common in older patients with inherent lung disease. In such systems, high vacuum levels are required to remove such volumes of air. During normal respiration, a negative pressure is developed, with respect to atmospheric pressure, in the pleural space. This is the result of the lowering of the diaphragm and the increased volume of the chest with the rise of the rib cage during inspiration. The normal value of the negative pressure is 3.5-8.0 centimeters of water. The volume flow of air is governed by the Hagen-Poiseuille Law which states that for a given pressure gradient and tube length, the determinant of flow rate is the radius of the tube. Anesthesiologists are acutely aware of this and breathing circuits in anesthesia are maintained as large and short as possible. When a tube ends in an abrupt manner in a chamber, the flow is no longer laminar but becomes turbulent which introduces added resistance to flow. The length of the tube (or pathway) is also important when vacuum is applied.
According to the formula: ##EQU1## Where D is tube diameter
L is length of tubing pathway PA2 C is air flow in Liters/Minute
For example:
L=2.5 ft. flow=28.9 L/min PA1 L=4.5 ft. flow=14.5 L/min PA1 L=10.0 ft. flow=7.2 L/min
Therefore, the optimum removal of air through a chest drainage device will occur when the largest tubing diameter is combined with the shortest pathway from the pleural space to the vacuum outlet. In addition, a minimum of abrupt changes from laminar flow to turbulent flow should interrupt the pathway.
The prior art devices do not meet these criteria. The pathway is by a series of connected chambers each of which contributes turbulence. Tubing pathways are unnecessarily long and in some cases, constructions are utilized to control flow or pressure all of which makes high vacuum a necessity to remove a given volume of air. Since the normal negative pressure required to keep the lung inflated and allow normal respiration is low, high vacuum negates the normal respiratory efforts. High vacuum can trap the lung against the intra pleural catheter thus occluding the catheter making the catheter ineffective and resulting in collapse of the lung. In addition, high vacuum overcomes the attempt of the lung tissue to seal itself thus causing the air leaks to continue or to increase. In applicant's earlier U.S. Pat. No. 4,738,672, a thorax drainage apparatus is disclosed which represented a significant advance in the art. However, it is believed that the instant invention represents a significant improvement over applicant's earlier patent. The standard method of vacuum control for chest drainage devices is by means of a column of water which is open to the atmosphere by means of a tube immersed to a depth equal to the amount of vacuum desired such as disclosed in the '672 patent. When that amount of vacuum is exceeded, atmospheric air enters the chamber and bubbles to relieve the excess vacuum. While this simple and effective method has been used successfully in the relatively stable environment of the hospital, it does have a disadvantage in a mobile environment especially when rapid transport is necessary. In the '672 patent, a simple chest drainage device was described which was admirably suited for such use. The device of the instant invention completes the requirements of stability without the hazards of a water column.